Sept. 29 (UPI) — Humberto strengthened slightly on Monday, bringing threats to the U.S. East Coast and Bermuda, the National Hurricane Center said.

Humberto had maximum sustained winds of 145 mph, the National Hurricane Center said in its 11 a.m. AST update.

It was located about 340 miles south-southwest of Bermuda and was moving northwest at 13 mph, according to the forecasters.

Hurricane-force winds extend outward up to 70 miles from the center of the storm, and tropical-force winds extend outward up to 185 miles.

A tropical storm watch was in effect for Bermuda. While Humberto is expected to miss the island, its residents could begin to feel the effects of tropical-storm-force winds starting late Tuesday, the NHC said.

“On the forecast track, the center of Humberto will pass west and then north of Bermuda on Tuesday and Wednesday,” the NHC said.

The storm is expected to experience fluctuations in intensity over the next day or so, but gradual weakening is forecast after that. It is, however, to remain a “dangerous major hurricane” over the next few days, according to the forecasters.

Swells generated by Humberto will continue affecting portions of the northern Leeward Islands, the Virgin Islands, Puerto Rico and Bermuda through much of this week, and likely produce life-threatening surf and rip current conditions.

Dangerous surf conditions were expected to begin affecting much of the U.S. East Coast on Monday.

Humberto is the eighth named storm of the Atlantic season and became the season’s third hurricane on Friday morning.

On Sunday, it was joined in the Atlantic by Tropical Storm Imelda.